There has been an increase in demand for the use of carbon fibers year by year, and the demand has been shifting from premium usage, such as for airplanes and sports equipment, to general industrial usage, such as for construction, civil engineering, and energy.
In general industrial usage, particularly in processes such as weaving, filament winding, pultrusion, and the like for forming large structural materials, a high fineness of approximately 100,000 deniers is required. Currently, in order to meet the demand described above, several yarns of approximately 7,000 to 20,000 deniers are combined to perform the formation.
Under the circumstances, if large packages having high fineness and heavy winding weight are obtained, the number of mountings of carbon fibers onto a higher processing apparatus will decrease and the creel unit will be more compact, and thus, great advantages are expected in the use of carbon fibers.
It is a first object of the present invention, in order to satisfy the demand described above, to provide a large package and a large packed member in which carbon fibers having particularly high fineness are wound so that the occurrence of trouble or inconvenience will be prevented during use.
On the other hand, with respect to the formation by combination, since there are distances between combination units, irregular impregnation of a resin may occur.
Also, since it is difficult to vertically layer fibers, fibers are horizontally combined, and thus, the thickness of the yarn will be the thickness of the combination unit, i.e., 7,000 to 20,000 deniers, and it is difficult to increase the thickness of the yarn. In particular, when a large and thick forming member is produced, the number of layers and the number of windings must be increased, resulting in disadvantage also in terms of formation time.
In other words, if a package of carbon fibers having a large number of filaments and large thickness is obtained, the number of mountings of carbon fibers onto a higher processing apparatus will decrease, formation time will be reduced, and the creel unit will be more compact, all of which are advantageous.
However, differing from general organic fibers, carbon fibers have significantly high Young's modulus and lack stretchability, and thereby, the range of windable tension is significantly small. If the tension is too low, trouble may easily occur, such as breaking at both sides of a roll, deformation due to external force, and slipping of a yarn layer out of a bobbin, and if the tension is too high, damage to yarns during winding, and deterioration of unwinding characteristics occur, and thus it has been technically difficult to set winding conditions with respect to cheese winding.
With regard to a carbon fiber package that does not easily break or does not have much fuzz during unwinding, a package has been disclosed in Japanese Patent Publication No. 62-46468, in which the package is a square-end type, and carbon fibers are taken up onto a bobbin with a given wind ratio, the wind angles of the fibers at the start of winding and at the end of winding are 10.degree. to 30.degree. and 4.degree. to 12.degree. respectively, and there is a shifting ratio of 50 to 150% of the average yarn width in relation to the already wound yarn, every 1 to 9 traverses. This package is a so-called "open-wind" package, in which, by minimizing the degree of overlapping of yarns, fuzz during unwinding and broken yarns are prevented. In the case of a bobbin having a given size, if the "open-wind" is used, as the yarns having a large number of yarns, that is, having high fineness, and having large thickness are wound, the spaces resulting from the overlap between yarns increase and the unevenness of the winding surface increases, and thus, the resultant package will be soft with low winding density, and both sides of the roll will easily bulge because the yarns are pushed out of the sides by means of winding tension and pressure on the winding surface (bearing pressure). Such a package may suffer broken winding during transportation, and because the bulge at both sides exceeds the length of a bobbin, the yarns may be damaged during the setup onto higher processing equipment.
It is the second object of the present invention, in view of the problems described above, to provide the most suitable shaped package with respect to winding of carbon fiber yarns having particularly high fineness, in which high winding density is obtained and breakage does not easily occur, by basically changing the form of winding.